Shining Mew - Probably second to Shining Charizard in popularity for shining cards, but the most recognizable Japanese-exclusive promo
The dungeon cards wont need to be drafted or included as part of either players deck, starting alongside each player's sideboard without taking up a sideboard slot
Rubberbanding can also be caused by improper installation of the game or if your game has corrupted files
We have two things: Pikachu as a highly collectible card for being one of the most famous in the franchise (above Charizard with ease) and for the art, which in addition to being secret, involves some Pokmon that marked this generation in the Sword/Shield block such as Inteleon, Zacian, Hisuian Zoroark, Crobat, Urshifu, Shadow Rider Calyrex, which, curiously, were cards that played well or were essential at some point in these almost 5 years of block